The present invention relates to a bypass turbo-fan type turbojet engine thrust reverser. In such engines, a duct is provided downstream of the fan to channel the so-called cold, bypass air exhausting from the fan. The duct consists of a fixed structure or fan nozzle having an inner surface which surrounds the engine proper and an outer wall, the upstream portion of which may be an extension of the surface of the portion of the cowling which surrounds the fan. The fan nozzle may channel both the bypass flow and the so-called hot, primary flow exhausting from the rear of the engine proper (in which case the hot and cold flows may be either mixed or confluent) or may channel only the bypass flow when so-called separate flows are involved.
The exterior of the casing surrounding the fan may be faired by an aerodynamically shaped wall minimizing powerplant drag as may the inner surface of this casing, the inner surface comprising the outer containment surface of the duct. This applies in particular to powerplants mounted on the outside of the aircraft, especially when these powerplants are attached under the wings or affixed to the rear of the fuselage.
Herein "external cowling" is intended to denote the assembly constituted by the exterior wall of the cowling of the powerplant.
FIG. 1 of the attached drawings shows a known embodiment of a thrust reverser of this type used in a bypass turbo-fan type turbojet engine while FIG. 2 shows a partial schematic perspective view of the same engine and thrust reverser installation.
The known thrust reverser is comprised of movable doors 7 which are part of the external cowling when they are in their inactive closed position during forward-thrust operation of the engine. Fixed upstream cowling portion 1 constitutes part of the external cowling which is upstream of the doors 7 and a downstream fixed cowling portion 3 is located downstream of the doors 7. Beams 18 located between the doors 7 connect the downstream external cowling portion 3 to the upstream external cowling portion 1. The doors 7 are mounted about the circumference of the external cowling and are pivotally mounted so that they may rotate about an axis located at an intermediate zone along or adjacent their side walls on the beams 18 which are adjacent to the side walls of these doors. The doors 7 are constructed so that the inner and outer surfaces of the doors are joined into a single unit by these side walls as well as by end walls located at the upstream and downstream ends of the doors. The outer surfaces of the doors constitute part of the outer cowling surface when the doors are closed, while the inner surfaces of the doors constitute part of the outermost surface of the duct wall, that is, an inner surface of the cowling.
The upstream portion 1 of the fixed cowling structure comprises a forward frame 6 which supports a control means which drives the doors 7 and which, by way of example, may be linear actuators 4.
Upon being driven open during transition to a reversed thrust position, the doors 7 pivot in such manner that the portion of each door which is downstream of its pivot axis is moved to more or less fully obstruct the duct while opening a passage to the exterior of the cowling and to deflect the bypass flow radially outward relative to the duct axis. In the open (thrust reversed position) the upstream portions of the doors 7 project outside the external cowling on account of constraints on the dimensions of these passages which must be designed and dimensioned to pass the flow without degrading engine performance. The excursion range of the doors is adjusted to allow passage of the cold bypass flow between the beams 18 and to suppress the forward thrust from this flow and to generate a counter-thrust produced by a redirection of this flow with an upstream flow component. The French patent documents 1,482,538 and A 2,030,034 describe such known embodiments.
Lastly, while the use of a linear actuator to drive the doors from one position to another is known, note should be taken of the very simple design whereby each door includes its own linear actuator affixed at its upstream end to the stationary upstream portion of the external cowling and at its downstream side to the upstream door portion in the manner described, for example, in French patent 1,482,538.
In general, the door 7 of this type of thrust reverser is complemented by a set of baffles which help channel the reverse flow when the thrust reverser is in the reverse thrust position and the door 7 is in the open, i.e., reverse thrust position. In particular, such a set of baffles may be represented by baffle 13 (FIG. 1) mounted on the upstream end of the door and consisting of a front portion which may or may not be provided with side parts. In order that the door 7 in its open, reversed thrust position will attain adequate performance, it is typically necessary, for instance in the known thrust reverser shown in FIG. 1, that the front portion of the inner panel 11 move away in a radially outward direction from a surface indicated by the line 14, which corresponds to a preferred boundary for the bypass flow as indicated by the arrow 15. A cavity 16 is defined on the duct side of the door 7 when the door is in the closed position corresponding to the forward thrust mode of operation. This cavity is bounded at the front by the door baffle 13 and by the flow deflecting edge 8 of the fixed upstream cowling portion 1, to the rear by the surface of the front portion of the inner panel 11; and by the inner surface of the door and the theoretical surface 14. In this arrangement, part of the flow in the duct is forced by the baffle edge 8 into said cavity 16, resulting in flow distortion or turbulence and aerodynamic losses which degrade forward thrust operation.
The French patent document A 2,618,853 solves this problem by canceling or minimizing the cavity 16 in the door 7. A moveable and retractable door lip or spoiler is driven by the door actuator into a position such that the door end projects beyond the spoiler to obtain maximum performance during forward thrust operation.
This system cooperates with the rod of the linear actuator to drive the doors 7 or with an automatic spoiler drive means. At the first motion of the doors during opening of the doors, the spoiler moves out of the door end either progressively, such as when the spoiler is driven by the said actuator, or fully when the spoiler is automatically driven by a spring system.
This design suffers a major drawback in that part of the cross-section of the thrust-reversal flow is masked during the initial opening of the door, whereby engine performance may be degraded during the intermediate thrust-reversal phase.